A so-called two-roller type fixing apparatus is typical used in recent electrophotographic systems. The two-roller type fixing apparatus comprises a fixing roller having thereinside a halogen lamp serving as heat-generating means, a pressing roller in rotational contact with the fixing roller, and a biasing member for allowing the pressing roller to be brought into press contact with the fixing roller at a given pressure. The two-roller type fixing apparatus is operable to allow a sheet with a surface supporting an unfixed toner thereon to pass through the rotational contact region along one direction so as to fix the unfixed toner onto the sheet.
In the two-roller type fixing apparatus having the above structure, the area of the rotational contact region is inherently apt to be increased as the fixing apparatus is increased in size, for example, in fixing apparatuses compatible with A-3 size sheets (or A4 cross-feed). In addition, when the fixing apparatus is designed to provide a wider nip width for achieving enhanced fixing performance, it is required to fairly increase a spring force which acts on both ends of the pressing roller.
The increased spring force can cause axial recurvation in the pressing roller itself and axially uneven press-contact force between the pressing and fixing rollers, resulting in deteriorated fixing performance against the intended purpose.
Further, if the press-contact force between the pressing and fixing rollers is increased, the increased press-contact force will act as an additional load against the rotation of the fixing roller, which leads to increased driving force, resulting in increase in apparatus size and/or energy consumption.
Various problems are involved in the above method of assuring the press-contact force by the increased spring force to provide a wider nip width. Thus, there is a strong need for providing an improved fixing apparatus free from such problems.